Summary

Discarding

One thing that our model still lacked was discarding. Given that discarding was such a big concern in both the west coast and gulf of Mexico push towards ITQs I think it’s time to implement it. This is in fact the last item to develop before I can fully simulate our OSMOSE Gulf of Mexico.

Imagine an easy 2-species logistic model. The two species (red and blue fish) are not geographically separated and fishers’ gear catches both at the same rate. There are 100 fishers. We run POSEIDON 10 times and show the dynamics below. With no regulations we average about 300,000 units of fish caught for each species. There is some discard (about 10%) which is not strategic: it’s just that the usual parameters have very small boats that often catch more than they can carry (throwing surplus overboard).

Imagine now we institute a TAC like we usually do: if any of the fish is caught above the quota level, all fishing stops. Imagine we put a very unequal quota of 200,000 red units and only 25,000 blue units. Also assume there are observers on all boats so that discard is impossible. Since fishers can’t avoid catching the protected (blue) species, the landings end up being only 25,000 units of each species. There is slightly more discards however due to the fact that when the season ends there are boats that had caught fish but not brought it to port yet and which they can’t sell as well as catches of species 1 that were brought to port but whose quota had been exhausted.

Weak TAC

Now we introduce a new policy similar to the season closures in pre-2007 Gulf of Mexico reef fisheries. The idea is that each species has a quota and when that quota is exhausted you are not allowed to land that fish anymore but you are still allowed to go catch other species. This “weak” form of TAC means that if you are in a scenario like ours where choosing target species is impossible, you are pushing fishers to discard.

Imagine then we impose the same TAC numbers as above,but once blue fish quota is exhausted, fishers can still go out and catch red. Since blue fish caught is dead weight, they discard all the unsellable fish as soon as they catch them.

The end result is that agents fill up both quotas every year, at the cost of huge discard rates (about 80%) for the protected blue fish.

What if we get smart and decide to ban discarding and put observers on all boats? Actually very little changes. Now discarding doesn’t happen on site, but fishers keep coming back with boats full of blue fish they can’t sell but they have to legally unload before going back to catch more. Discard happens at port rather than at sea.

The only real difference in fact is that now fishing became a lot less profitable

Because agents need to go back and forth rather than fishing on the spot.

ITQ

Now one common fear for tradeable quotas is that they incentivate discarding. Here, rather than evolving the probability of discarding, I am just going to run 10 simulations where fishers can’t discard and 10 when they can.

Same biology, same 100 fishers, same quota numbers as above but this time we split the quota and let people trade. When there are observers on the boat and consequently no discarding we get more or less back at the original TAC result: most of the red quota is unfished because the blue quota runs out. There is quite a lot of non-strategic discard in ITQ simulations though due to fishers going out and catching more than the quota they actually own and not being able to buy quotas in time.

If we remove observers and fishers are allowed to discard we get that both quotas are filled due to very high discard rates for the protected species:

For the ITQ scenario it’s actually interesting to study also the price of quotas over the years. With no discarding we get again the result of blue quotas being more expensive than blue fish sale price (10$). With discarding instead both quotas prices are below sale price. Red quotas are barely traded when there are observers (since they are rarely binding), but they are traded a lot (and at high prices) when there is discarding. Volume of trades is a lot higher with discarding simply because there is so much more fishing overall.

Average Results

This is a summary of all the results: